Fuel Pump Relay Switch Wiring Diagram

Upgrading your vehicle's fuel system is often a necessary step when increasing horsepower. This is usually done with a larger fuel pump, fuel lines, and better filtration than the factory components. If you are adding fuel injection to a carbureted vehicle or need more flow than a mechanical pump allows, then you need to an electric fuel pump. Most of fuel injection systems supply a signal feed for the pump to power on, but this is not suitable to actually power up the pump, rather it is a trigger for a relay system. If you are adding an electric pump to carbureted vehicle, you won't have any power source at all. The fix for these issues is a fuel pump relay kit.

While you could source a relay and wire it all up yourself, most hobbyists tend to shy away from wiring, and for good reason – it is complicated and one mistake can burn your car to the ground. The solution is a relay kit from Painless Performance. The kit we used comes with the relay, wiring, and a automatic resetting circuit breaker to keep things safe. There is plenty of wire in the kit to locate the relay at the rear of the vehicle and run it to a front-mounted battery in most vehicles. This item can be special ordered from your local NAPA AUTO PARTS store.

The Painless Performance relay kit comes with everything you need for most installations.

Key Components

Power Source – To make the pump work, you need 12 volts of sparky goodness. This is sourced direct to the battery. Avoid any other sources unless it is a auxiliary battery post. You don't want to add current draw to an existing circuit, which could overload it. The source needs to be fused as close to the battery as possible, within 18 inches. This is to minimize the potential for fire in the event the power were grounds out.

This is the circuit breaker. Instead of a fuse, this system auto-resets when the fault goes away, so a blown fuse won't leave you on the side of the road.

Trigger – A 12-volt trigger is required to activate the relay. This is most often a positive trigger, but a negative trigger can also be used. There are three common sources for the trigger; the ECM, switched ignition, or a manual switch. If you are using a fuel injection system, then you need to use the fuel pump signal as the trigger for the relay. For carbureted engines, you can connect the relay to a switched ignition source (must have power in both start and run key positions), or you can simply wire in a manual switch. This provides you with a little added security, as a hidden switch makes the vehicle much harder to steal.

The large red wire is the battery feed, the large yellow wire is the power output. The black wire is the trigger ground, and the small yellow wire is the trigger positive.

Output – The output is the power feed that runs to the pump itself.

Ground – While many people take the ground for granted, a good ground is critical for proper operation. Electricity flows from negative to positive, not the other way around. The ground must use the same capacity wire as the feed and it must be a good connection. The easy part of the ground is that the chassis itself is usually a good ground. Make sure that your vehicle has a good ground wire or strap from the battery to the engine, chassis, and to the body itself. Modern vehicles are mostly glued together, so adding those ground straps goes a long way to eliminating ground loops issues. The pump and the relay can share the same ground point.

We mounted the relay to the interior of the trunk, the ground was connected at the mounting point as well.

Installation

The relay in the Painless kit is an all-weather unit, meaning it can be mounted in any position and can be mounted outside the vehicle. In our install, we located the relay in the trunk for easy access. We drilled a small hole (and used a grommet for protection) to run the power wire to the pump itself. The fuel pump on this vehicle is an aftermarket in-tank pump. To make servicing easy, we connected the pump power and ground wires with spade-type disconnect terminals. This allows the fuel tank to be removed without cutting wires or fighting the terminal nuts on the pump itself.

The power wire goes directly to the pump, and the pump is grounded to the chassis. The relay ground was connected to the screw that was used to secure the relay itself to the body inside the trunk. We stripped the paint from the grounding point on the chassis and in the trunk to ensure that the ground is good.

We terminated the power feed to the pump using a quick-connect. This allows for easy removal for service without risking the threads on the pump.

The signal and power feeds were run through the interior of the car and connected under the hood. This car has a carbureted engine, so we connected the power feed and ignition feed to the starter relay under the hood. The starter relay has a battery lug that connects straight to the battery, so this is a good source. The ignition switch point has 12-volts when the key is in the run and start position, so the pump will be powered on while the engine is cranking, you need that.

The wires were fed through a grommet in the trunk floor.

The trigger wire was connected to the starter solenoid ignition post.

To keep things simple, we connected the power feed to the battery post on the starter solenoid as well.

The entire fuel pump relay kit installation takes about 2-3 hours, depending on how much interior you have to remove. If you run the wires under the car, extra care must be taken to prevent the wires from being damaged. Heat and road debris can make for a really bad day when it comes to wiring, so be careful to secure dangling wires and protect them from heat and debris.

Check out all the electrical system products available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on installing a fuel pump relay kit, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Wikimedia Commons.

Jefferson Bryant View All

A life-long gearhead, Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin', Mopar Muscle, and many more. Jefferson has also written 4 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.

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